Patent Document 1 discloses a main casing having an inlet and an outlet, and an impeller disposed rotatably inside the main casing. Such a centrifugal compressor further includes a supply pipe for supplying a cleaning liquid for cleaning the impeller, and a cleaning-liquid injection nozzle for injecting the cleaning liquid supplied from the supply pipe to the surface of the impeller, disposed on the inlet side of the main casing. With such a centrifugal compressor, dust adhering to the surface of the impeller is washed off by the cleaning liquid.